From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The utility and correct installation of a voltmeter on the electrical system.
| Identifier | WestWitteringFiles\P\2July1926-September1926\ Scan081 | |
| Date | 21th August 1926 | |
| UTILITY OF A VOLTMETER ON THE ELECTRICAL SYSTEM. It has been suggested that we were provided with a fairly accurate voltmeter on the chassis electrical system, trouble due to high voltage and overcharging of the battery might be materially reduced. Though this may be true to some extent we do not think it would be so to an extent sufficient to justify the presence of an additional expensive electrical instrument. Assuming that the voltmeter is connected between the positive terminal of the dynamo and the chassis frame (see Note below), it is true that its indications may be of considerable value if correctly interpreted, but as there are various factors at work tending to raise or lower this voltage, considerable discretion is called for in such interpretation. Contd. Note:- This would appear to be the correct way of connecting the voltmeter, i.e. better than connecting it across (a) Dynamo terminals, (b), Battery terminals, (c) Lamp terminals, because connected thus, it is capable of shewing the operating voltage of the system in all circum- stances without the necessity of an additional (voltmeter) switch which is not the case in either (a), (b), or (c) above. Connected thus, and with dynamo not cut in, the voltmeter would indicate the voltage of the battery either on open circuit or when supplying the lamps, via. the main charging switch, and its circuit would be "off" and not absorbing current until the charging switch were put "on". Thus the charging switch itself would provide the means of switching on the voltmeter when the car is at rest. When the car is running, with charging switch on the voltmeter would indicate the voltage of the system as now raised by the charge, but with charging switch "off" there would be no indication. To shew the voltage of the battery when supplying the lamps without charge it would be necessary to be below dynamo cutting-in speed. | ||